Method of treating natural silk



Patented May 29, 1928.

UNITED STATES 1,671,786 PATENT OFFICE.

SAMUEL S. SADTLER, 0F SPRINGFIELDTOWNSHIP, MONTGOMERY COUNTY, AND v ELBERT C. LATHROP, 0F PHILADELPHIA, PENNSYLVANIA.

METHOD.OF TREATING NATURAL SILK.

No Drawing.

Our invention relates to the methods or processes of treating natural or raw silk,

such as is obtained from the cocoons of the.

Bombyr mori, and more particularly to the softening process preparatory to twisting or throwing the filaments and. one of the objects of the invention is to standardize and regulate the softening process, with a view of imparting to the silk a predetermined degree of softness which is or may be needed or desired in the finished product for which the silk is intended to be used, or which may particularly adapt it for the manufacturing process to which it is to be subjected, or for any other reason.

Thus, one of the objects of our invention is to enable one to so treat one lot or batch of raw or natural silk that it will possess with certainty, that degree of softness an other properties, required or desired by a manufacturer who may knit the silk into his particularproduct on his machines, and to another lot or batch a different degree of softness and quality particularly desired by another manufacturer for making a different product or the same product manufactured on a different type of knitting machine, and to so standardize the process and treatment that the same predetermined desired characteristics may be always obtained by a control of the softening process to which the silk is subjected.

Heretofore raw, natural or real silk filaments have been softened preparatory to throwing or twisting by sub ecting the silk to an aqueous bath containing soap and oils, and wherein theoils are emulsified or dispersed by the soap. Such baths present a milky appearance. Sulphonated oils have also been used in these baths in lieu of the soap, or of the oil, or of both of them. In these baths, heretofore used, the soaps of simple fatty acids, or the sulphonated oils, gradually dissociate in water,.and impart to the bath that alkaline characteristic or property whichseems to be essential to the proper softening of silk- Moreover, the presence on the silk fibers, after treatment, of the oils and soaps or other substitutes, such, for example, as the more or less neutralized sulphonated fatty acids, seems also to be necessary to the softened silk. In softening processes heretofore practised, the softening liquid or bath is never used for a second time as far as we are aware. It is Application filed June 1. 1925. Serial No. 34,165.-

thrown away after one batch or quantity of silk has been treated in it.

Our invention comprises certain improvements in the softening baths and the method and manner in which the same is compounded or prepared so that it may be repeatedly used and practically standardized.

Further objects of our invention are to so treat the silk that the soft wet threads are stronger thanthose produced by the prior softening processes and methods above described; to provide a bath which may be used repeatedly by adding to the used and partly spent liquor enough fresh liquor to compensate in volume for. that retained by the softened silk; and to reduce the amount or quantity of sericin removed from the silk by the softening bath.

In carrying out our improved process, we may first use any good silk softening liquor as for instance one consisting of water,

neutral castile soap and a substantially neutral fatty oil, such as neutral olive oil or neutral neats-foot oil. In such a bath, the oil is readily emulsified, the soap dissociates to a considerable extent and produces a certain alkalinity to the solution, the net intensity of the alkalinity of which can be readily determined by estimatingthe hydrogen lon concentration (pH, Sorensens scale). In a fresh well selected commercial softenlng bath the intensity of the alkalinity is presumably correct. This liquor may be used to soften silk in the ordinary way. But after such a bath has once been used to soften a batch of silk, it has heretofore been thrown away as waste, for the concentration of the hydrogen ion is increased and therefore the pH value will have. substantially changed and become less (smaller). It is generally necessary for the bath to have a hydrogen ion intensity, as determined by the pH scale of measurement which will render the bath as alkaline or slightly more alkaline than that WhlCh 1t is desired that the treated silk shall have. It may be readily seentherefore that the mere addition of any amount of fresh bath liquor to used or partly spent liquor wouldnot result in the production of a bath having thesame intensity of alkalinity, or pH, that the prior or original bath had. By the practice of our invention, however, such spent or partially spent liquors may be repeatedly used.

As a concrete example of our novel method or process, we give the following:

soap. The silk may be soaked in this bath d for from 4 to 6 hours at tained at about 100 F.

At the end of this treatment the silk may be removed from the bath and placed in a suitable centrifugal hydro-extractor by which the free spent or partially spent liquor contained in the silk is removed. This separated liquor may be put back in the tank or vat in which the silk was softened and then fresh liquor may be added to bring the bath up to therequired volume. The

a temperature main- 7 hydrogen ion intensity of the bath will be Increased and, as determined by the pH scale of measurement, the H value will now be somewhat lower than t at of the preceding or original bath. We may now add to the liquor in the tank enou h of a suitable alkaline solution to bring the bath to substantially the same hydrogen ion intensity that the original bath had, provided, of course, the second batch of silk is to ssess the intensity of the hydrogen ion (p that the prior batch had. Generally, the hydrogen ion concentration of the bath would have to be changed only a fraction of one H value by the addition of a suitable alkaine agent to renew the bath.

As an alkaline solution to be added to the spent or partially spent bath we may use a solution of sodium hydroxid, sodium carbonate, or of sodium potassium carbonate or. any similar alkaline solution to bring the. intensity of the hydrogen ion to the desired point on the pH scale. v

But it is not to be understood that the invention comprises merely the brim ing the intensity of the hydrogen ion of t e spent bath to that of the original bath, for it may thus be readily brought to anydesired point of the pH that may be adapted for softening raw silk.

Different batches of softened silk may be so treated as to make them have different values of the hydrogen ion (pH) by varying the intensity of the alkalinity of the ordinarv fresh softening baths or of baths containing partially spent liquor. For some purposes we may produce softened silk in which pH=7.5 while for other pur ses we may produce silks in which p =8; or pH=8.5; or pH=9 or any other number of the Sorensen scale, by merely changing or adjusting the intensity of the alkalinity of the softening bath. When, therefore, for instance a pH=7.5 silk is desired, enough of the alkaline solution should be added to the fresh bath, or to the partially spent bath or to a mixture of the two to change the hydrogen ion intensity of the bath and bring the pH value up to pH=7.5 and preferably a little above pH=7 .5, for it has been found that the pH value of the bath should generall vbe slightly higher than the plH value 0 the silk desired to be prouce It is not to be understood that the silk softened by this new soap, oil and alkaline solution bath above described, will be like that produced by the first or original soap oil bath, above described, or by any of the old and well known soap and oil mixtures above referred to. The silk produced by this new bath will be stronger, and will contain more sericin, than that produced by the old processes, for after the bath has been re-used three or four times, the amount of sericin removed from the silk treated therein will build up in the bath until it becomes a substantial and constant quantity. The result of this is that thereafter much less sericin will be removed from the silk in the bath. The amount of sericin in the bath after the third or fourth use will be substantiall constant, probably because the bath has ta en from the silk all the sericin that it can, and is robably ractically saturated therewith. 8 sericin will therefore remain on or in the softened silk, than remains thereon after treatment by the old processes, thus producing a stronger, less stretchy filament than one-from which more sericin has been removed.

Thus, the presence of a comparatively slight, but eventually substantially constant amount of sericin in the softening bath contributes to the production of a new, better, stronger, more uniform silk filament. But if it is found desirable to diminish from the very first the amount of sericin removed from the silk, without waiting until the bath shall have accumulated it by repeated use, sericin or other albumenoids, such as casein or gelatin may be added to the original bath with similar results, namely, that a comparatively little sericin will be abstracted from the silk by the bath during the softening process.

We also wish to make it clear that when we refer in the specification and claims to the pH value of the bath as being substantially the same as the pH value of the silk after treatment therein, we do not mean that the pH value of the bath must be exactly like that of the resulting silk but that the pH value of the bath may be a few points, or enough, higher to compensate for any drop which may occur between the pH value of the bath and the pH value of the resulting silk, to which reference has already been made above. Since this drop or difference is usually only a fraction of one pH value, the pH value of the bath and onsidera ly more of theof the silk produced by treatment therein, may be regarded and appropriately described as being substantially the same, for the purposes of this disclosure.

In the practice of this improved process, there does not appear to be any limit to the number of times the liquor may be re-used, if fresh liquor be added to maintain the volume, particularly, if some preservative, such as sodium salieytate is added to the bath, to prevent decomposition. The practice of this invention results in a very great saving of the amount of silk softening liquor required, and for a plant wherein thousands of pounds are treated daily, and the liquor is used for but one batch, this novel process could be practised to great advantage.

Having thus described our invention, what we claim and desire to protect by Letters Patent of the United States is:

1, The method of softening natural or raw silk which consists in subjecting a batch of such silk to a normal softening bath liquor, removing thesilk therefrom when 1t has been completely treated and softened therein, adding to the partially spent liquor enough normal fresh softening bath liquor to compensate for the volume carried away by the silk last previously treated in said partially spentliquor, and adding thereto a sufficient quantity-of an alkaline solution to increase the pH value thereof suitable for softeninga fresh batch of silk without injury thereto.

2. The method of softening raw natural silk which consists in adding to a partially spent softening liquor suflicient fresh liquor to replace that carried away by the silk last previously treated therein, adding thereto a quantit of an alkaline solution sufficient to make tlie intensity of the alkalinity of the bath (Sorensen scale) substantially the same as that which it is desired that the silk shall have after treatment therein, and softening a fresh batch of raw natural silk therein.

3. The method of softening raw natural silk which consists in adding to the partially spent softening liquor sufficient fresh liquor to replace that carried away by the silk last previously treated therein, adding thereto a quantity of alkaline solution suflicient to bring the intensity of the,alkalinity of the bath up to a predetermined point of the Sorensen scale suitable for softening a fresh batch of raw silk without injury thereto, immersing a fresh batch of-raw silk therein to for from 4 to 6 hours andmaintaining the temperature of the bath during such treatment at substantially 100 Fahr.

4. The method of softening raw silk by repeatedly using the bath liquor which consists 1n adding to the partially spent liquor after a batch of silk has been softened therein, a sufiicient quantity of fresh liquor to compensate for that lost in the previous use of the spent liquor, adding thereto an alkaline solution in an amount sufficient to increase the pH value thereof to substantially that which the next batch of silk to be treated shall have, softening a fresh batch of raw silk therein, removing said silk from said bath when the softening thereof is completed and adding fresh liquor to the remaining partially spent liquor, adding thereto an alkaline solution sufiicient to increase the pH value thereof to substantially that which the next batch of silk to be treated therein shall have, and repeating the steps substantially ad infinitum.

5. The method of producing a bath for softening raw natural silk to produce a softened silk having a predetermined hydrogen ion concentration which consists 1n adding to a standard softening bath a sufiicient amount of alkaline solution to increase the pH value of the bath to a point substantially the same as that which is to characterize the silk after it has been subjected to a softening treatment therein.

6. The method of producing a bath for softening raw natural silk to produce a softened silk having a predetermined hydrogen ion concentration which consists in adding to a standard softening bath a sufficient amount of alkaline solution to make the pH value of the bath substantially the same as that which is to characterize the silk after it has been subjected to a softening treatment therein, and adding'a small amount of an albumenoid thereto.

7. The method of treating spent liquor of a silk softening bath which consists in add-.

ing theretov a relatively small quantity of fresh liquor, then adding thereto a suflicient alkaline solution to produce therein a hydrogen ion substantially the same as that which is to characterize the silk after treatment therein.

8. A bath for softening raw natural silk comprising a mixture of partially spent silk softening liquor and fresh silk softening liquor, and a sufficient amount of an alkaline solution to produce therein a hydrogen ion intensity substantially the same as that which the silk to be treated therein is desired to possess.

9. The method of treating partially spent liquor which has been previously used to soften raw silk and to make it available for reuse, comprising the adding to said spent liquor a relatively small amount of fresh softening liquor, adding a sufficient quantity of an alkaline solution to bring the intensit y of the hydrogen ion pM Sorensen scale) to substantially that which is to characterizc the silk after treatment therein.

10. The method of treating partially spent liquor which has been previously used to soften raw silk and to make it available for re-use, comprising the adding to said spent silk after treatment therein, and adding asr'nall quantity of an albumenoid thereto.

11. The method of producing a softened silk having a predetermined hydrogen ion value (pH Sorensen scale) which consists 10 in adding to a normal softening bath an alkaline solution in a suflicient quantity to raise the intensity of the'alkalinity to said predetermined oint of the Sorensen scale.

In witness w ereof, we have hereunto set 15 our hands this 29th day of May, 1925.

SAMUEL S. SADTLER. ELBERT C. LATHROP. 

